what can science tell us about marine reserves?

A recent review of the most up-to-date scientific information about marine reserves, spearheaded by PISCO, revealed global trends in the effects of marine reserves. Considerable research—from over 200 publications in peer-reviewed journals—provides a clear picture of what has happened after the establishment of marine reserves.

As of 2010, scientists have studied more than 150 marine reserves in at least 61 countries around the world and monitored biological changes inside the reserves. The number of species in each study ranged from 1 to 250 and the reserves ranged in size from 0.006 to 800 square kilometers (0.002 to 310 square miles).

What are marine reserves?

Marine reserves are ocean areas that are fully protected from activities that remove animals or plants or alter habitats, except as needed for scientific monitoring. Most marine reserves are established with the goal of increasing the abundance and diversity of marine life inside the reserve. Scientific research shows that marine reserves consistently accomplish this goal.

As indicated in the graph above, a 2009 study documented a wide range of changes inside marine reserves, but nearly all of the effects were positive. This global review of peer-reviewed marine reserve studies revealed that fishes, invertebrates, and seaweeds had the following average increases inside marine reserves:

Biomass, or the mass of animals and plants, increased an average of 446%.

Density, or the number of plants or animals in a given area, increased an average of 166%.

Body Size of animals increased an average of 28%.

Species Density, or the number of species, increased an average of 21% in the sample area.

These increases were similar between tropical and temperate reserves, indicating that marine reserves can be effective regardless of latitude.

Heavily fished species often showed the most dramatic increases. Some fished species had more than 1000% higher biomass or density inside marine reserves. Even small changes in species diversity and individual body size are important. These two indicators have less potential for change than do biomass or density. Additionally, in some studies such as ones conducted in Florida, USA and Kenya, reserves produced greater increases than MPAs that allowed some fishing.